Porous media, particularly microporous membranes, are used to filter a variety of fluids. During the course of filtering fluids, the porous media eventually become clogged or plugged with impurities and/or other fluid components. This is particularly a problem in the filtration of protein-containing fluids. Natural proteins, such as those in milk, beer, and wine, can quickly plug porous media such as microporous membranes. In the filtration of such protein-containing fluids, it is typically desirable to maintain a constant filtrate flow through the porous medium by increasing the upstream pressure over time. As a result, however, pore clogging increases, and the flow through the porous medium becomes impeded, at an exponential rate. Thus, even though fluid can perhaps be passed through the porous medium with a high upstream applied pressure, e.g., more than 15 psi, the effective life of the porous medium is essentially over when an undesirably high upstream pressure, e.g., about 5-10 psi or so, is required to maintain satisfactory filtrate flow through the porous medium.
While a clogged filtration medium can be replaced, the costs involved in such replacement can be quite significant. Thus, many techniques have been developed to unclog porous media. These unclogging techniques, however, may damage porous media, particularly microporous membranes, or leave contaminants in the porous media if not thoroughly washed prior to reuse. In addition, both the replacement of porous media and the unclogging procedures typically involve halting the filtration process, thereby resulting in potentially significant and undesirable downtime in the filtration process.
Accordingly, there remains a need for a method of filtering a protein-containing fluid through a porous medium, particularly a microporous membrane, such that clogging of the porous medium is forestalled and filtration downtime is reduced. Such a method should also provide for an increased period of time during which useful filtration of a protein-containing fluid can be carried out, without a significantly increased upstream pressure to maintain a constant filtrate flow through the porous medium. Furthermore, such a method should not run the risk of damaging the porous medium or of introducing contaminants into the porous medium and/or fluid being filtered by the porous medium. The method of accomplishing these desirable conditions should also be such that it can be efficiently and economically used. The present invention provides such a method of pretreating a porous medium used to filter a protein-containing fluid through a porous medium.
These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.